1. Field of the Invention
The present invention relates to a character signal display for a camcorder, and more particularly, to a character signal display that utilizes a synchronous signal supplied by a camera and a viewfinder as a synchronous signal for displaying a character signal, when no external video signal is input.
Korean Patent Application Nos. 93-14810 and 94-17905 are incorporated herein by reference for all purposes.
2. Discussion of Related Art
Generally speaking, a user can confirm the operational status of equipment in use by displaying characters on a display device such as a monitor or an electronic viewfinder. The user can also select a desired function using the displayed characters. The function whereby characters are displayed on the screen of a display device is called an on-screen display (OSD) function. The OSD function is widely applied to such devices as televisions and camcorders for displaying images. It will be noted that vertical and horizontal synchronous signals are employed to permit display of OSD character data onto an exact location of a screen. The vertical and horizontal locations of the character data on the screen are determined by the vertical and horizontal synchronous signals.
FIG. 1 is a block diagram showing a conventional camcorder character signal display which performs the above-mentioned OSD function.
In FIG. 1, a camera 10 is connected to a first character combiner 20 which is connected to a first input terminal of a selector 31 of a recorder/reproducer unit 30. An external video signal input terminal 3 is connected to a second input terminal of selector 31. Recorder/reproducer unit 30 includes a selector 31, a recorder 32 connected to the output terminal of selector 31, a reproducer 33, a first control switch 34 having a first select contact connected to the output of recorder 32 and a second select contact connected to the input of reproducer 33 and whose output terminal is connected to a head 35, a second control switch 36 having a first select contact connected to the output terminal of selector 31 and a second select contact connected to the output of reproducer 33, a second character combiner 37 connected to the output terminal of second control switch 36, and a composite synchronous signal separator 38 connected to the output of second character combiner 37. A third character combiner 40 is connected between second character combiner 37 and an electronic viewfinder 80.
A microcomputer 60 is connected to each control terminal of selector 31 and first and second control switches 34 and 36. Microcomputer 60 is also connected to input terminal of a character signal generator 70. First, second and third outputs of character signal generator 70 are connected to first, second and third character combiners 20, 37 and 40, respectively. Character signal generator 70 receives vertical and horizontal synchronous signals from a synchronous signal separator 90. One input of synchronous signal separator 90 is connected to the output of composite synchronous signal separator 38, while another input is connected to the output of a synchronous signal generator 95.
The camcorder character signal display constructed as described above can be roughly divided into a camera (10), a VCR and electronic viewfinder (80). The recorder/reproducer unit 30, third character combiner 40, microcomputer 60 and character signal generator 70 belong to the VCR.
A detailed constitution of camera 10, which permits conversion of optical information into an electrical video signal input to first character combiner 20, is shown in FIG. 2, wherein object information input via a lens 11 a is converted into an electrical video signal in a charge-coupled device (CCD) 13 through an optical low-pass filter (LPF) 12. LPF 12 prevents interference among the pixels of CCD 13. In a preprocessor 14, the output of CCD 13 is correlated-double-sampled and automatically gain-controlled. Gamma correction is also performed in preprocessor 14 so as to correct the color component of the video signal with respect to the gain-controlled output. In an analog-to-digital (A/D) converter 15, the output of preprocessor 14 is converted into a digital signal. Then, a digital signal processor (DSP) 16, including a synchronous signal generator 16a which generates a synchronous signal. The video signal output from A/D converter 15, separates the received signal into luminance and chrominance signals for processing. Thereafter, the processed video signal and the generated synchronous signal are combined to form a composite video signal, which is output via a digital-to-analog (D/A) converter 17. In addition, DSP 16 has a timing generator so that the timing of CCD 13, preprocessor 14 and A/D converter 15 can be controlled and so that a vertical driver 19 for driving CCD 13 can be properly controlled by the generated vertical synchronous signal (Vsync).
It will be appreciated that DSP 16 and motor driver 11b are controlled by microcomputer 18. It will also be appreciated that, while microcomputers 18 and 60 are separate elements, a single microcomputer providing all processing functions can be employed.
Accordingly, the output of camera 10 shown in FIG. 1 is a composite video signal in which an image signal and synchronous signals are combined. In first character combiner 20, first character data output from character signal generator 70 is combined with the composite video signal. Here, the first character data is used during recording. For example, the character data may indicate various recording conditions (e.g., filming date, location, subject) which can be used, after editing. Thus, a user can recognize specific recording conditions using the first character data.
The output signal of first character combiner 20 (called the camera video signal) is input to the first input terminal of selector 31, while an external video signal is input to its second input terminal via external video signal input terminal 3. The external video signal source may be a video cassette recorder, another camcorder or a television.
Selector 31 permits selection of either the external video signal or the camera video signal according to an internal/external input select signal (int/ext) output from microcomputer 60. The selected signal is applied to recorder 32 and the first select contact of second control switch 36. In addition, according to a record/reproduction mode control signal CTL1 output from microcomputer 60, first control switch 34 controls whether the output signal of recorder 32 is recorded via head 35 or the signal reproduced by head 35 is provided to reproducer 33. In second control switch 36, either the output signal of selector 31 or that of reproducer 33 is switched in by a reproduction/non-reproduction mode control signal CTL2 output from microcomputer 60.
Furthermore, in second character combiner 37, the second character data generated from character signal generator 70 is combined with the video signal switched by second control switch 36, so as to be output to a monitor (not shown) and third character combiner 40. The output of second character combiner 37 is also provided to composite synchronous signal separator 38 which, in turn, separates a composite synchronous signal loaded onto the composite video signal from second character combiner 37, for subsequent output to synchronous signal separator 90. The second character data generated by character signal generator 70 is to be displayed onto a monitor and is data concerned with channel number, volume level and the like.
Third character combiner 40 combines the video signal output from second character combiner 37 and the third character data generated from character generator 70. The third character data is for display onto electronic viewfinder 80 and is data regarding, e.g., camcorder operating conditions, charge state, etc.
In electronic viewfinder 80, as shown in FIG. 3, the video signal output from third character combiner 40 (FIG. 1) is displayed onto display means 89 through first and second amplifiers 81 and 82. At the same time, the vertical and horizontal synchronous signals loaded onto the composite video signal output from third character combiner 40 are separated in vertical and horizontal synchronous signal separators 83 and 85. Then, in vertical and horizontal synchronous signal oscillators 84 and 86, the respectively separated synchronous signals are input so as to generate the synchronous signals Vsync and Hsync having the proper frequency. Here, an automatic frequency controller (AFC) 87 is utilized in conjunction with horizontal synchronous signal oscillator 86, to provide a stable output. In accordance with the vertical synchronous signal (Vsync) and the horizontal synchronous signal (Hsync) output from the synchronous signal oscillators 84 and 86, the vertical and horizontal deflections of the display means 89 are controlled by a flyback transformer 88, so that the output of second video amplifier 82 can be displayed onto a correct location.
Character signal generator 70 shown in FIG. 1 generates first, second and third character data for first character combiner 20, which combines recording character data, for second character combiner 37, which combines OSD character data for monitor display, and for third character combiner 40, which combines OSD character data for electronic view finder 80, respectively, under the control of microcomputer 60. It will be noted that a synchronous signal is needed for displaying the above character data onto a screen. Accordingly, the vertical and horizontal synchronous signals are input to character signal generator 70, to thereby establish the location of the displayed character data.
Procedures for providing a synchronous signal to the conventional character signal generator 70 can be explained as follows, with respect to two types of video signal input conditions.
(1) Given that an external video signal or a camera video signal is input, the synchronous signal loaded onto a composite video signal output from second character combiner 37 is separated by synchronous signal separator 90 via composite synchronous signal separator 38. Thus, the horizontal and vertical synchronous signals are output to character signal generator 70.
(2) When an external video signal is not input but the selected mode is an external mode, the synchronous signal internally generated by synchronous signal generator 95 is input to synchronous signal separator 90. Synchronous signal generator 95 includes an oscillator for generating precise synchronous signals, which is typically a costly crystal oscillator. The input synchronous signal is divided into a vertical sync signal and a horizontal sync signal in synchronous signal separator 90, and are then output to character signal generator 70. When these horizontal and vertical synchronous signals are provided to character signal generator 70, the character signal is displayed onto a predetermined location of a monitor or electronic viewfinder 80, under the control of microcomputer 60 via the data output to character signal generator 70.
Since the conventional character display device as described above is constituted by synchronous signal separator 90 and synchronous signal generator 95 for supplying character signal generator 70 with needed synchronous signals when no external video signal is input, the overall cost of the camcorder cannot be reduced.
In addition, when the synchronous signal of synchronous signal generator 95 is divided into vertical and horizontal synchronous signals and supplied to character signal generator 70, the supplied synchronous signals are erratic. This disrupts and detracts from proper character data display. Although synchronous signal generator 95 generates a clean, steady synchronous signal, the input video signal has an imperfect horizontal synchronous signal and/or vertical synchronous signal because when a VCR-reproduced video signal is input, the horizontal and vertical synchronous signals loaded thereon may have been reproduced under such conditions as a poor video tape or irregular capstan motor operation. Accordingly, the composite video signal combining the video signal and the character data cannot be displayed on the correct location of the monitor or the electronic viewfinder. As a result, the displayed characters are not sharp.